Asymmetric Friedel-Crafts Alkylations Catalyzed By Bifunctional Cinchona Alkaloids
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example 1
General Procedure for Friedel-Crafts Addition of Indoles to α-Ketoesters
[0290]At room temperature to the solution of pyruvates 3a-d (0.2 mmol) in Et2O (0.4 mL) was added Q-1d or QD-1d (10 mol %) and followed by addition of indoles (0.4 mmol). Then the mixture was let stand at room temperature for 40-72 hours (as indicated in Table 1, entries 1-10). The reaction mixture was subjected to flash chromatography to afford the desired product 4. For entries 12 and 14 in Table 1, 0.02 mL of Et2O was added to the reaction mixture. For entries 13, 15, 17, 18, these reactions were carried out at 70° C. in 0.02 mL of t-butyl methyl ether (TBME). For entries 16, the reaction was carried out at 70° C. in 0.05 mL of t-butyl methyl ether (TBME). See FIG. 3.
example 2
General Procedure for Friedel-Crafts Addition of Indoles to Aldehydes
[0291]At room temperature to a solution of the aldehyde (5a-d) (0.2 mmol) in TBME (0.02 mL) was added Q-1d or QD-1d (10 mol %) and followed by the addition of the indoles (0.4 mmol). Then the mixture was allowed to stand at room temperature for 4-72 hours (as indicated in Table 2, entries 1-6) or at 70° C. for 40-48 h (entries 7-8, Table 2). The reaction mixture was subjected to flash chromatography to afford the desired product 6. See FIG. 4.
example 3
Data for Products 4 and 6
[0292]
[0293](−)-4Aa was obtained in 89% yield as a foam after flash chromatography (elution solvent: Ethyl Acetate / Hexanes=1 / 3) and 87% ee as determined by HPLC analysis [Chiralpak AD, Hexanes:IPA, 75:25, 1.0 mL / min, λ 220 nm, t (minor)=14.2 min, t (major)=7.7 min] from a reaction catalyzed by Q-1d (10 mol %) at room temperature for 63 hours. [α]D25=−1.8 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.14 (br, 1H), 7.76 (d, J=8.0 Hz, 1H), 7.44-7.42 (m, 1H), 7.34-7.32 (m, 1H), 7.19 (t, J=7.2 Hz, 1H), 7.11 (t, J=7.2 Hz, 1H), 4.39-4.31 (m, 1H), 4.17-4.09 (m, 1H), 4.07 (s, 1H), 1.29 (s, 9H), 1.21 (t, J=7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 172.5, 136.8, 124.4, 123.9, 122.2, 120.2, 119.8, 115.7, 111.3, 93.8, 77.2, 68.9, 63.0, 30.7, 27.5, 13.8; IR (CHCl3) ν 3408 (br), 3058, 2970, 2242, 1731, 1619, 1543, 1458, 1255, 1033; HRMS (CI) m / z calcd. for (C18H21NO3+H+): 300.1599, found: 300.1592. (+)-4Aa was obtained as a foam in 96% yield and 88% ee from a reaction catalyzed...
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